1. Field of the Invention
The present invention relates to a printing apparatus for printing by ejecting ink from an ink head and having a correcting unit for correcting sheet feed accuracies.
2. Description of the Related Art
In a conventional printing apparatus for printing by ejecting ink from the ink head, while the ink head is being moved in a main scanning direction, ink is ejected from the ink head and a sheet is conveyed by a predetermined unit distance in a sub scanning direction, so that the sheet is printed by further repeating the ink ejection.
In the sheet conveying, if the predetermined unit distance cannot be maintained every sheet conveying, the image overlapping (black streak) and the image spacing (white streak) are produced, so that printed image quality cannot be maintained.
Therefore, in the conventional printing apparatus, a method for maintaining the printed image quality has been known as follows. The error in sheet conveying is stored in a storing unit as a correction value, and the correction value is added to the sheet conveying distance so as to have a new conveying distance. Then, the sheet is conveyed by the new conveying distance so as to maintain the conveying accuracy.
For example, a conventional printing apparatus has been known as follows. First, a test pattern is printed so as to determine the sheet conveying distance correction value for storing it. Then, the conveying correction value is added to the sheet conveying distance so as to have a new sheet conveying distance. In the printing apparatus, the sheet is conveyed in accordance with the obtained sheet conveying distance so as to correct sheet conveying accuracies (Japanese Patent Laid-Open No. 2003-11345, for example).
The sheet conveying distance accuracies largely differ depending on the sheet kind and factors such as a frictional coefficient.
Hence, there has been known a method for switching a conveying correction value to be added to a conveying distance every sheet kind used for printing, each sheet kind having its correction value stored in a printing apparatus using the conveying correction value.
However, in the method disclosed in Japanese Patent Laid-Open No. 2003-11345 for storing the conveying correction value, when the conveying correction value is stored every sheet kind, the sheet kind cannot be determined whether it is corrected or uncorrected.
Thus, during printing, the sheet kind to be printed cannot be determined whether it is corrected or uncorrected, resulting in being printed without correction so as not to maintain the printed image quality.